Field of Invention
This invention relates to an air supply system and in particular to an air supply system for supplying pressurized air from a compressor to operate a range of functions on a tractor such as a tiliterre pressure control system (TPCS).
Description of Related Art
The tire pressure on a tractor is often adjusted by a TPCS when moving between a field and a road to improve the tractor's efficiency and to reduce the pressure on the field which in turn reduces soil compaction and damage to crops.
A typical air supply system on a tractor therefore supplies air from the compressor to a primary consumer (such as the tractor's braking system) via an air dryer and also to a secondary consumer such as a TPCS which may be supplied via a dryer or directly to the tire. Some on board air consumers may be provided with a respective reservoir. It is desired that the adjustment of the pressure of the tires is done as quickly possible to save time when moving between a field and a road. This also includes the tires of attached trailers which may be connected to the air supply system and the TPCS of the tractor.
To save energy, an air compressor is switched to an idle mode when the consumer air reservoirs reach a predetermined pressure level. In an idle mode the air flow is discharged to the atmosphere so that the input power of the compressor is reduced, thus increasing efficiency. When the pressure in a consumer air reservoir falls below the predetermined level the compressor is switched to the normal supply mode.
When inflating the tires, the air compressor must constantly supply air as the volume of a reservoir associated with a tire is relatively small compared to the volume of the tire. As a consequence, the air stored in the reservoir would not be sufficient to inflate the tire without the compressor running. For example, a rear tire may have an interior volume of up to 1600 liters, whereas the reservoir can only store 160 liters. This results in that during inflation, the compressor is not likely to be switched into an idle mode.
Pressure measurements are typically conducted several times during inflation/deflation processes. The time taken to measure the pressure of each tire can take several seconds. During pressure measurements, a small volume of air from the compressor is needed to activate pilot valves to connect the compressor to a tire valve. During a tire pressure measurement, as a consequence of this air consumption, the predetermined pressure level in a reservoir results in the compressor being switched into an idle mode. This is the case even if the desired pressure of the tire has not been reached. Thus, after each pressure measurement, the compressor must then be switched back from the idle mode to the normal supply mode, if the tire is to be pressurized again. This extends the length of time needed to deflate and inflate the tire, as each measurement switches the compressor into an idle mode.